Metal woking process



`1an. 12, 1932. c. R. SHORT 1,840,641

METAL WORKING PROCESS Filed March 27. 1926 Patented Jan. 12, 1932 p UNITED STATES PATENT oFFlcE.

LHABLES R. SHORT, F DAYTON, OHIO, ASSIGNOR TO GENERAL MOTORS RESEARCH COR- PORATION, OF DETROIT, MICHIGAN, A. CORPORATION OF DELAWARE METAL woxING PRocE-ss Application led March 27, 1926. Serial No. 97,949.

There are now on the market self-lubrieating bushings and bearings of porous compositions which will hold a sufficient quantty of oil to properly lubricate the bearing surfaces for a long period of time. It has been found difficult to machine bearings of this character for the reason that ordinary grinding and cutting methods result in dragging the relatively soft metal of which the bearing is made, filling the pores, thus diminishing its lubricant holding capacity, and, in some cases, stretching the wall of the bushing and' thereby increasing the diameter of the hole. An additional diiiiculty encountered where inding is resorted to is that the surface ogrthe grinding wheel is quickly illed with particles of bearing metal rendering it ineffective. Where the bearing is of a rather hard composition as in the case of the porous bronze bearing sold under the tradename of Durex, the edge of the cutting tool is quickly dulled and as the bearing must be accurately sized it is necessary to frequently replace the cutting tool,an item of considerable expense.

In an effort to overcome the above difficulties it has been proposed to size the bearing 'to proper outside dimensions by the use of a plain roller. This was found to be unsatisfactory for the reason that many of the bearings were cracked and broken as a result of the improper-,application of heavy pressures.

I have found that by using a roller of special design for the final sizing operation I am enabled to secure accurately sized bearings with a low percentage of fractures. Thus my roller is so constructed that high unit pressures are produced locally which have the effect of causing a slight flow of metal from the pressure areas to the areas not under pressure. The bearing or bushing is thus reduced to the'required size without deformation or stretching of the bushing' Wall. This method has the further advantage that the roller is subject to very slight deterioration in use.

While I have described above the application of my improved method to the working of a special type of article, that is, porous bushings, it is to be understood that it is ofl general utility in the treatment of parts where very slight reduction in size is desired. Thus it may be used for sizing sheets, rods, and the like.

The invention is described on the accompanying drawings in the form which it would assume in the treatment of articles of substantially cylindrical shape, but it is to be understood that' it is subject to considerable modification in the treatment of different kinds of articles.

In the drawings:

Figure 1 is a plan view of a lathe showing my improved device in use in the treatment of the outer surface of a porous bushing.

Figure 2 is a sectional view showing a slightly modified form of apparatus.

Figure 3 is a plan view of the roller used in Figure 2.

In Figure 1 the reference character 2 indicates a lathe of conventional construction upon the mandrel 4 of which is secured the b ushing 6. The bushing is fixed upon the mandrel in any suitable manner, so as to rotate therewith. 8 indicates an adjustably mounted bracket having a forked end 10 in which is journaled the roller 12 of special design. In the form shown in Figure l the roller 12 carries a spiral thread 14.

In operation the bracket 8 is adjusted to force the thread 14 of the roller 12 against the bushing with sufcient pressure so that when the lathe is operated the diameter of the bushing will be reduced tothe size desired. This necessitates a very careful adjustment of the position of the roller, and if desired, the rolling operation may be performed in a number of steps each of which effects a slight reduction in the outside diameter of the bushing. With the parts positioned as described, the lathe is now operated, the bushing 6 and roller 12 rotating in contact with each other after the manner of two intermeshing gears. By providing the roller with a spiral thread instead of a plane surface pressure is applied to the 'bushing throughout a plurality of local areas which are constant- 1y shifted as the rotation continues. The v gaps between the threads allow room for a slight flow of metal from the areas which are subjected to pressure and this action is of importance'in avoiding the fractures which result where pressure is applied throughout the length of the bushing.

In Figures 2 and 3 I have shown a modification of the roller. In these iigures the spiral thread 12 is interrupted to provide teeth 20. This constitutes a further localization of pressure and allows greater room for iow of metal from the parts subjected to compression. With this type of roller it is desirable that the roller and bushing be of different diameters so that the teeth on the roller will not strike the bushing at the same place on each revolution. It is apparent that the configuration of the roller may be greatly varied. Other arrangements of teeth may be used. The areas of the tops of the teeth may be varied within wide limits to secure any desired degree of localization of pressure. In the case of an uninterrupted thread the width and pitch of the thread may be changed as desired.

The above described operation produces a properly sized bushing without fracturing the metal or destroying the porosity of the 1n supporting it on a mandrel in pressure contact with a helically grooved sizing roller, preventing axial movement of said cylindrical member on the mandrel while in engagement with said roller, and rotatably driving one of said engaging members while they are in engagement.

4. The method of reducing the outer diameter of a hollow cylindrical member of substantially non-plastic material, comprising telescoping said member on a mandrel and fixing it rigidly in place thereon, rotating said mandrel on a fixed axis and progressively forcing a helically grooved sizing roller laterally upon the exterior of said hollow member while said hollow member is held against axial movement, whereby the outer diameter of said hollow member is reduced without change in the interior dimension thereof.

In testimony whereof I affix my signature.

CHARLES It. SHORT.

bearing surface. There is at the same time no possibility of producing stretching of the bushing wall and consequent variation in the inside diameter of the bushing.

While the invention has been described in its application to the sizing of a cylindrical bushing, it is obvious that the same method can be used for the outside finishing of two cylindrical bearing segments, such as the interchangeable halfbearings commonly used in automobile engines.

This invention has been described in its application to the exterior sizing of porous bushings but it is by no means restricted to this use. It is of utility. wherever a part is to be accurately sized or slightly reshaped.

I claim: A

1. The method of reducing the outer diameter of a hollow cylindrical member of substantially non-plastic material which consists in supporting it on a mandrel in pressure contact with the entire length of a helically grooved sizing roller throughout the operation and rotatably driving one of the engaging members while said members are held in engagement. v

2. The method of reducing the outer diameter of a hollow cylindrical member of substantially non-plastic material which consists in supportingit on a mandrel in pressure contact with a helically grooved sizing roller, rotatably driving one of the engaging members while they are in engagement and preventing relative axial movement between the cylindrical member and the roller.

3. eter of a hollow cylindrical member ofsubstantially non-plastic material which 'consists The method of reducing the outer diam- 

